Calculate how many months it takes to recover your Customer Acquisition Cost from each new customer. See how gross margin, ACV and CAC interact — and what the capital implications are at scale.
CAC payback period is the number of months until a new customer generates enough gross profit to recover their acquisition cost. It is the primary determinant of how capital-efficient your growth is. At 6-month payback you can reinvest recovered capital in the next quarter. At 24-month payback, you need 2 years of revenue per customer before you break even — requiring significant external capital to fund growth.
If your CAC is £3,600 and payback period is 18 months, you need £3,600 of capital tied up per customer for 18 months before recovery. Adding 15 new customers/month: £3,600 × 15 × 12 = £648,000 of annual CAC spend before any recovery. For a company with 24-month payback adding 50 customers/month: £CAC × 50 × 12 = potentially £10M+ of capital required just for customer acquisition, before overheads.
Four levers: (1) Increase ACV through better positioning, packaging or pricing (directly reduces payback); (2) Improve gross margin by reducing COGS/infrastructure costs; (3) Reduce CAC through better conversion rates and cheaper acquisition channels; (4) Annual upfront billing — receiving a full year of ACV upfront immediately improves cash flow even if the economic payback period is unchanged.
Switching customers from monthly to annual billing dramatically improves cash efficiency even without changing economic payback. A £600/month customer on annual billing pays £7,200 upfront — meaning payback is immediate in cash terms if ACV > CAC. Offering a 10–20% discount for annual payment is almost always worth it for the cash flow improvement and lower churn.
CAC payback period = CAC / Monthly Gross Profit per Customer. Monthly Gross Profit = (ACV / 12) × Gross Margin. Example: CAC £3,600, ACV £7,200, gross margin 72%: Monthly GP = £600 × 72% = £432. Payback = £3,600 / £432 = 8.3 months. This is the number of months until each customer has returned their acquisition cost in gross profit — after which they generate positive contribution.
Benchmarks: under 12 months is best-in-class (Bessemer Venture Partners benchmark), 12-18 months is good, 18-24 months is acceptable but requires significant capital, above 24 months is very capital-intensive. Enterprise SaaS with large contracts often has longer payback (18-24 months) but compensates with higher LTV:CAC ratios. Consumer/PLG SaaS should target 6-12 months.